Reason I say tank water is the in how tannins work. Tannins very readily bind to organic matter. Your tank water is chock full of biowaste and leached proteins from fish waste/plant waste/etc. Tannins will leach out of the wood only to join back up with the wood to replace other tannins that leach into the water table. If you have tank water it will lock the tannins down so when you change the water the tannins will leave the wood more quickly, significantly shortening the leaching process.
Great piece of driftwood. If the slight yellow bothers you seachem purigen will remove it right away .
I collected nicely shaped local driftwood year later still floating outside lol so used mopani wood for my tanks . Water was brown till added purigen in filter .
From what I understand, and of course this is depending on the quantity, type of plants and light requirements, fish do not put off enough Co2 to supplement a tank. Med to high light tank will need Co2.